I assume that's because of lack of VRAM space, which can't really be helped unless you're willing to completely overhaul the art loading scheme (like, using dynamically reloaded patterns rather than pattern load queues - dunno if that's even possible in S1).

Rika claims he ported the entire Tails object... Then he must have added extra flight. Swimming, while cool, would be extra-extra. I doubt he'd put the swimming in a higher priority than the tails though.